(1) Field of the Invention
This invention relates to agricultural irrigation and more particularly to irrigation systems having elevated horizontal elongated pipes carrying water under pressure, moved by vehicles traverse to their length, with a plurality of sprinklers dispersing water therefrom. Those persons making, using, or selling agricultural irrigation systems of this type have ordinary skill in this art.
(2) Description of the Related Art
Farmers recognize that the best way to water most crops is by a slow steady rain with large drops which are absorbed by the soil without packing or collapsing the soil and without damaging erosion.
Agricultural systems using elevated horizontal elongated pipes carrying water under pressure supported by vehicles which move the pipes transversely of its length and dispersing water therefrom by a plurality of sprinklers are well known to the art.
Many patents show such types of systems as well as them being commercially available upon the market. Systems are generally divided into two categories, one being designated as center pivot system and the other being designated as a rectilinear system.
Before this invention, many systems used drop tubes from the elevated horizontal pipe so that the sprinkers would be lower. It is desirable to have the sprinkler located as close to the top of the growing crop as suitable for operation. I.e., in the case of alfalfa, cotton, or beans, the sprinkler might be no more than 1 to 2 feet above the ground. In the case of grain sorghums, the sprinkler might be located 4 to 5 feet above the ground (1 foot above the top of the gram sorghum). In the case of corn, it might be desirable to have the sprinklers 7 to 8 feet above the ground, again, about 1 foot above the top of the crop at the time it was being irrigated. Using the same system for different crops and using the same system at different times of the year when the crops are at different heights, it is desirable to change the system. Certain drops have been developed to support the sprinkler below the horizontal pipe. Some of these systems had telescoping metal tubes somewhat like a slide trombone that could be clamped at different positions.
When there was not so much need to conserse the water used by such systems nor the need to conserve the energy used to pump the water at high volumes and high pressures, normally the systems operated at high pressures and the sprinklers to sprinkle water from such systems were high pressure sprinklers. Also, in many instances the water was dispensed from the system in fine sprays or mists which were subject to evaporation and also the distribution of the water was badly effected by wind. I.e., a sprinkler producing a fine mist distributed water in a pattern which was easily distored by the wind. By "high pressure" it is meant that the pressure at all sprinklers is at least 50 psi.
However, at the present time there is a great need to conserve both the quantity of water used and the energy used to pump the water. To conserve energy, it has been found desirable to use low pressures. By "low pressure" it is meant that the pressure at all sprinklers is less than 35 psi.
In recent years, low pressure spray nozzles on steel drop pipes are being widely used instead of impact sprinklers on top of the pipe. (Escalating energy cost have brought on this trend) However, the low pressure sprays often have 4-5 times the application rates of impact sprinklers (10-15 foot diameter versus 50-60 foot diameter). There is a growing need for a low pressure sprinkler that saves energy without sacrificing the benefits of broader coverage; and therefore, much lower application rates. Lower application rates enable the user to slow down the system and apply larger applications without exceeding the intake rate of the soil. For example, a 2 inch application instead of a 1 inch application also enables the operator to make fewer passes of the equipment over the field.
Senninger Irrigation, Inc., of Orlando, Fl. makes and distributes off center rotary action sprinklers which is shown in U.S. Pat. No. DES. 253,364 which issued Nov. 6, 1979. The sprinklers are sold under the trademark "THE WOBBLER", and are called jitter sprinklers herein. This type sprinkler is characterized by distributing water over an area of 45' to 50' in diameter at flow rates from one gallon per minute to 10 gallons per minute with a pressure of 20 psi. or less at the sprinkler. The different flow rates are obtained by using nozzles from 3/32 inch to 3/8 inch. The sprinklers have a random vibration or a jitter action to obtain an exceptionally good pattern of distribution. The water is dispensed in large drops and, because of the large diameter spray pattern, is applied slow enough to be absorbed by the soil without packing or collapsing the soil and without damaging erosion.
Difficulty has been experienced in using jitter sprinklers upon elevated horizontal elongated pipe moveable irrigation systems. Jitter sprinklers tended to damage the system because of their vibration and shock. In many cases, the vibration and shock caused the collapse of the system which resulted in manufacturers not recommending the use of this sprinkler. We have eliminated this problem by using a flexible hose for a drop to completely dampen all vibrations to the sprinkler system. Conventionally all low pressure sprays have been located downward. We allow the use of upright sprinklers (jitter or impact) in an upright position but below the pipe.
Senninger Irrigation, Inc. recognized the problems of the destructive nature of the vibrations and always recommended that "THE WOBBLER" sprinklers be mounted securely in an upright position. The manufacturer recommended that it be securely mounted on steel risers no higher than 4 feet above the ground level. Also, Senninger advertised "THE WOBBLER" as being particularly suited for solid set irrigation. This indicated to applicants that "THE WOBBLER" was not suitable for irrigation systems using movable elevated pipe.